Many miles of buried, steel fluid transmission pipeline extend through urban areas where the earth's surface is paved with asphalt or concrete or various structures are disposed over the pipeline. Various types of fluid transmission pipelines and similar buried structures are required to employ cathodic protection systems to avoid corrosion of the buried metal. In this regard, a source of direct current (DC) is applied through the positive source electrode to a ground circuit, which may comprise a mass of buried steel or an abandoned pipeline, for example, and the negative electrode of the source is connected to the pipe or other structure to be protected so that the structure to be protected becomes the cathode in any electrolytic reaction with the surrounding soil and, thus, is not subject to electrolytic corrosion. Pipelines equipped with cathodic protection systems are usually tested from time to time to verify that a correct negative potential exists between the soil and the pipe to assure that the cathodic protection of the pipe is effective. However, pipelines running under urban areas present great difficulty in making the cathodic protection verification measurements.
For example, conventional practice in verifying the correct operation of a pipeline cathodic protection system comprises attaching one lead of a voltmeter to the pipe itself and the other lead to a suitable grounding or reference electrode in contact with the soil in the vicinity of the pipe. In some urban areas, access ducts or manholes are provided in the street or sidewalk pavement for access to the pipeline but access to the soil under the pavement in the vicinity of the selected measurement points for the pipeline is often difficult or impossible to achieve. Moreover, the presence of structures such as buildings, paved roadways and sidewalks, the associated pedestrian and vehicle traffic and the existence of regulatory requirements prohibit forming any type of hole in the pavement to gain access to the soil in the test area. Still further, the stringing of conductor wire between the pipeline access duct or manhole and a point of measurement where the soil is exposed is inconvenient and may be virtually impossible to carry out due to the distances required and the fact that the wire cannot be strung along the roadways or sidewalks in the aforementioned urban setting.
Accordingly, the aforementioned difficulties in testing pipeline cathodic protection systems to verify proper operation, particularly in urban areas, have heretofore made the test procedure unreasonably expensive and subject to delays due to regulatory requirements, and in some cases virtually impossible because of conditions which do not favor providing access to the soil through public and private asphalt or concrete roadways, other paved areas such as parking lots and sidewalks and, of course, through interior floors or walls of private or public structures. However, notwithstanding the difficulty of gaining access to the soil surrounding buried pipelines in such urban settings, the requirements to monitor such pipelines for proper cathodic protection still exist.
Certain types of electrodes or contactors have been developed which are intended to establish electrical contact with the earth through certain types of pavement. However, verification that a suitable conductive path has been established is difficult with such devices and the question remains as to whether or not a correct pipe-to-soil potential measurement can be made or confirmed when the reference electrode is disposed on a pavement surface above the soil in which the reference electrode is intended to be in electrically conductive engagement. Accordingly, there has also been a need to verify that proper electrically conductive engagement is established between the reference electrode and the soil in the vicinity of the pipeline so that measurement of the pipe-to-soil potential can be established. The present invention is directed to solving the above-mentioned problems in measuring the proper operation of cathodic protection systems for buried pipelines and other similar structures which are buried in the soil and for which cathodic protection systems are in use.